Etch rate uniformity using the independent movement of electrode pieces

ABSTRACT

A plasma reactor comprises a chamber, a bottom electrode, a top electrode, a bottom grounded extension adjacent to and substantially encircling the bottom electrode. The top grounded extension adjacent to and substantially parallel to the top electrode. The top electrode is also grounded. The top grounded extension is capable of being independently raised or lowered to extend into a region above the bottom grounded extension.

FIELD OF THE INVENTION

The present invention relates to semiconductor fabrication. Moreparticularly, the present invention relates to a plasma etchingapparatus.

BACKGROUND OF THE INVENTION

A typical plasma etching apparatus comprises a reactor in which there isa chamber through which reactive gas or gases flow. Within the chamber,the gases are ionized into a plasma, typically by radio frequencyenergy. The highly reactive ions of the plasma are able to react withmaterial, such as the dielectric between interconnects or a polymer maskon a surface of a semiconductor wafer during it being processed intoIntegrated Circuits (IC's). Prior to etching, the wafer is placed in thechamber and held in proper position by a chuck or holder which exposes atop surface of the wafer to the plasma.

In semiconductor processing, the etch or deposition rate uniformityacross the wafer during each process directly affects the device yield.This has become one of the main qualifying requirements for a processreactor and hence is considered a very important parameter during itsdesign and development. With each increase in the size of waferdiameter, the problem of ensuring uniformity of each batch of integratedcircuits becomes more difficult. For instance, with the increase from200 mm to 300 mm in wafer size and smaller circuit size per wafer, theedge exclusion shrinks to, for example, 2 mm. Thus maintaining a uniformetch rate, profile, and critical dimensions all the way out to 2 mm fromthe edge of the wafer has become very important.

In a plasma etch reactor, the uniformity of etch parameters' (etch rate,profile, CD, etc.) is affected by several parameters. Maintaininguniform plasma discharge and hence plasma chemistry above the wafer hasbecome very critical to improve the uniformity. Many attempts havebeen-conceived to improve the uniformity of the wafer by manipulatingthe gas flow injection through a showerhead, modifying the design of theshowerhead, and placing edge rings around the wafer.

One problem in a capacitively-coupled etching reactor is the lack ofuniform RF coupling especially around the edge of a wafer. FIG. 1illustrates a conventional capacitively-coupled plasma processingchamber 100, representing an exemplary plasma processing chamber of thetypes typically employed to etch a substrate. The plasma reactor 100comprises a chamber 102, a bottom electrode 104, a top electrode 106.The bottom electrode 104 includes a center bottom electrode 108 and anedge bottom electrode 110. Top electrode 106 includes a center topelectrode 112 and an edge top electrode 114. Edge top electrode 114 andedge bottom electrode 110 are in the shape of a ring respectivelyencircling center top electrode 112 and center bottom electrode 108 toform a single plane.

Center bottom electrode 108 is connected to RF power supply 118 whiletop electrode 106 and edge bottom electrode 110 are grounded fordraining charge from plasma 116 produced between top electrode 106 andbottom electrode 104. As illustrated in FIG. 1, the shape of the glowdischarge region (plasma 116) is distorted near the edge of centerbottom electrode 108 because of grounded edge bottom electrode 110. Thatdistortion causes non-uniform etch rate on a substrate (not shown)placed on center bottom electrode 108.

During plasma processing, the positive ions accelerate across theequipotential field lines to impinge on the surface of the substrate,thereby providing the desired etch effect, such as improving etchdirectionality. Due to the geometry of the upper electrode 106 and thebottom electrode 104, the field lines may not be uniform across thewafer surface and may vary significantly at the edge of the wafer 104.Accordingly, grounded ring 110 is typically provided to improve processuniformity across the entire wafer surface.

Because the parts in top electrode 106 are static, the etch rate cannotbe separately controlled at the center and at the edge of the wafer. Thenon-uniformity during the etching process can lead to differentdimensions between the center and the edge lowering the yield ofreliable devices per wafer.

Accordingly, a need exists for a method and apparatus for independentlycontrolling the etch rate at the center and the edge of a wafer. Aprimary purpose of the present invention is to solve these needs andprovide further, related advantages.

BRIEF DESCRIPTION OF THE INVENTION

A plasma reactor comprises a chamber, a bottom electrode, a topelectrode, a bottom grounded extension adjacent to and substantiallyencircling the bottom electrode. The top grounded extension adjacent toand substantially parallel to the top electrode. The top electrode isalso grounded. The top grounded extension is capable of beingindependently raised or lowered to extend into a region above the bottomgrounded extension.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of this specification, illustrate one or more embodiments of thepresent invention and, together with the detailed description, serve toexplain the principles and implementations of the invention.

In the drawings:

FIG. 1 is a diagram schematically illustrating a plasma reactor inaccordance with a prior art;

FIG. 2 is a diagram schematically illustrating a plasma reactor inaccordance with one embodiment.

FIG. 3 is a flow diagram schematically illustrating a method foroperating the plasma reactor illustrated in FIG. 2.

DETAILED DESCRIPTION

Embodiments of the present invention are described herein in the contextof plasma reactor. Those of ordinary skill in the art will realize thatthe following detailed description of the present invention isillustrative only and is not intended to be in any way limiting. Otherembodiments of the present invention will readily suggest themselves tosuch skilled persons having the benefit of this disclosure. Referencewill now be made in detail to implementations of the present inventionas illustrated in the accompanying drawings. The same referenceindicators will be used throughout the drawings and the followingdetailed description to refer to the same or like parts.

In the interest of clarity, not all of the routine features of theimplementations described herein are shown and described. It will, ofcourse, be appreciated that in the development of any such actualimplementation, numerous implementation-specific decisions must be madein order to achieve the developer's specific goals, such as compliancewith application- and business-related constraints, and that thesespecific goals will vary from one implementation to another and from onedeveloper to another. Moreover, it will be appreciated that such adevelopment effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of engineering for those ofordinary skill in the art having the benefit of this disclosure.

FIG. 2 illustrates one embodiment of a plasma reactor 200 comprising achamber 202, a bottom electrode 208, a bottom electrode extension 210, atop electrode 212, and a top electrode extension 214. In accordance withone embodiment, bottom electrode extension 210 includes a grounded ring210 parallel and adjacent to the bottom electrode 208 and encircling thebottom electrode 208. The top electrode extension 214 includes aadjustable grounded ring 214 parallel and adjacent to the top electrode212 and encircling top electrode 212.

Bottom electrode 208 is connected to RF power supply 218 while topelectrode 212, top electrode extension 214, and bottom electrodeextension 210 are grounded for draining charge from plasma 216 producedbetween top electrode 212 and bottom electrode 208. By way of example,bottom electrode extension 210 and top electrode extension 212 may bemade of a conductive material such as aluminum. As illustrated in FIG.2, plasma 216 includes two regions 220 and 222 having different plasmadensities based on the position (height) of top electrode extension 214.

Bottom electrode 208 is configured to receive a workpiece and includesan associated bottom electrode area that is adapted to receive theworkpiece. Bottom electrode 208 is coupled to at least one power supply218. Power supply 218 is configured to generate RF power that iscommunicated to bottom electrode 208. For illustrative purposes only, adual frequency power supply 218 may be used to generate the highelectric potential that is applied to a gas to produce plasma 216. Moreparticularly, the illustrated power supply 218 is a dual power frequencypower supply operating at 2 MHz and 27 MHz that is included in etchingsystems manufactured by Lam Research. It shall be appreciated by thoseskilled in the art that other power supplies capable of generatingplasma in the processing chamber 202 may also be employed. It shall beappreciated by those skilled in the art that the invention is notlimited to RF frequencies of 2 MHz and 27 MHz but may be applicable to awide range of frequencies. The invention is also not limited to dualfrequency power supplies but is also applicable to systems that havethree or more RF power sources with a wide variety of frequencies.

Top electrode 212 is disposed at a predetermined distance above frombottom electrode 208. Top electrode 212, top electrode extension 214,together with ground extension 210 are configured to provide a completeelectrical circuit for RF power communicated from bottom electrode 208.Top electrode extension 214 can move up or down independently from topelectrode 212 to manipulate plasma density at the edge of bottomelectrode 208—plasma region 222. With the plasma density varied at theedge of bottom electrode 208, the etch rate at that region can beindependently controlled (either faster rate or slower rate) from theetch rate in the plasma region 220. Those of ordinary skills in the artwill appreciate that there are many ways to lower and raise the topelectrode extension 214. For example, a mechanical or motorized knob maybe used to raise or lower top electrode extension 214 without having toopen and access the interior of chamber 202.

During plasma processing, the positive ions accelerate across theequipotential field lines to impinge on the surface of the substrate,thereby providing the desired etch effect, such as improving etchdirectionality. Due to the geometry of top electrode 212 and bottomelectrode 208, the field lines may not be uniform across the wafersurface and may vary significantly at the edge of the wafer.Accordingly, top and bottom electrodes extensions 214 and 210 areprovided to improve process uniformity across the entire wafer surface.

Plasma reactor 200 is configured to receive a gas (not shown) that isconverted into plasma 216 by plasma reactor 200. By way of example andnot of limitation, the relatively high gas flow rate that is pumped intochamber is 1500 sccm. Gas flow rates less than 1500 sccm as well as morethan 1500 sccm may also be applied.

To generate plasma 216 within chamber 202, power supply 218 is engagedand RF power is communicated between bottom electrode 208 and topelectrode 212. Gas is then converted to plasma 216 that is used forprocessing workpiece or a semiconductor substrate. By way of example andnot of limitation, RF power levels of 2 W per cm³ of plasma volume maybe applied. RF power levels of less than 2 W per cm³ of plasma volumemay also be applied.

For illustrative purposes, plasma reactor 200 described in FIG. 2employs capacitive coupling to generate plasma 216 in processing chamber202. It shall be appreciated by those skilled in the art, that thepresent apparatus and method may be adapted to be used with inductivelycoupled plasma.

Those of ordinary skill in the art will appreciate that the aboveconfigurations shown in FIG. 2 are not intended to be limiting and thatother configurations can be used without departing from the inventiveconcepts herein disclosed. For example, two or more adjacent topelectrode extension 214 may be positioned to further control the etchrate at the edge of bottom electrode 208.

FIG. 3 illustrates a method for using the plasma reactor illustrated inFIG. 2. At 302, the position (raised or lowered) of top electrodeextension 214 is selected. Top electrode extension 214 is capable ofbeing raised and lowered to extend into a region above the bottomelectrode extension. At 304, plasma reactor 200 processes a wafersupported by bottom electrode 208. At 306, the wafer is examined todetermine the etch uniformity throughout the surface of the wafer. At308, the position of top electrode extension 214 is adjusted based onthe analysis at 306 to further improve the etch rate uniformitythroughout the surface of the wafer.

While embodiments and applications of this invention have been shown anddescribed, it would be apparent to those skilled in the art having thebenefit of this disclosure that many more modifications than mentionedabove are possible without departing from the inventive concepts herein.The invention, therefore, is not to be restricted except in the spiritof the appended claims.

1. A plasma reactor comprising: a chamber; a bottom electrode and a topelectrode enclosed within said chamber; a bottom grounded extensionadjacent to and substantially encircling said bottom electrode; a topgrounded extension adjacent to and substantially parallel to said topelectrode; wherein said top grounded extension is capable of beingindependently raised and lowered to extend into a region above saidbottom grounded extension.
 2. The plasma reactor of claim 1 wherein saidtop grounded extension includes a ring.
 3. The plasma reactor of claim 1wherein said bottom grounded extension includes a ring.
 4. The plasmareactor of claim 1 further comprising a power supply coupled to saidbottom electrode, said bottom electrode configured to receive aworkpiece.
 5. The plasma reactor of claim 4 wherein said power supplygenerates a plurality of frequencies to said bottom electrode.
 6. Theplasma reactor of claim 5 wherein said top electrode is grounded.
 7. Amethod for using a plasma reactor having a chamber with a top electrode,a bottom electrode, a bottom grounded extension adjacent to andsubstantially encircling said bottom electrode, a top grounded extensionadjacent to and substantially parallel to said top electrode, the methodcomprising: adjusting a position of the top grounded extension, the topgrounded extension capable of being independently raised and lowered toextend into a region above the bottom grounded extension.
 8. The methodof claim 7 further comprising supplying power to the bottom electrode,the bottom electrode configured to receive a workpiece.
 9. The method ofclaim 8 further comprising generating a plurality of frequencies to thebottom electrode.
 10. The method of claim 7 further comprising groundingthe top electrode.